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Thomas Fournier

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Ok I have a 77 k20, rebuilt 350 th400 np241c with slip yoke. I have a fresh built drives shaft w/new Spicer factory style 1410 u-joints and 1410 slip yoke custom built for this truck. Also just had my 14bff rebuilt with a 1410 yoke 4.56 gears and a detroit. I re-welded my spring perches and set it 2 degrees lower than the t-case output so if the pinion walks up it will be perfect with the t-case. -6 degrees on the tcase and +4 degrees on the pinion. Here's the catch it only vibrates after 65+ it's a pulsing vibration and it's SUPER annoying to say the least. It's perfectly quiet at 55. It has a shackle flip with 56" springs with I believe 1 or 2 leaves taken out, overloads are still in. Could that 2 degrees be causing the vibration? I'm at a loss here. It's always done it with other trans and other tcase's but everything Is new and we're it should be, I don't think tires could cause this type of violent pulsating vibration. Other than this the truck is a dream. I've been chasing this for years now and I don't know of anything else that could cause this! I'm going to get my tires balenced next week, they are Falken 315 70 17 on aluminum rims very low miles.
Thanks for any help,
-Daniel
 

Fordum

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Factory new, or new built? I learned about built shafts the hard way in my old Ford. I needed a new rear shaft because the splines were worn, and there was a place in town called The Drive Shaft Shop. They would cut and weld in a new spline much cheaper than factory.

I asked when I got it back if they had balanced it, and they said that the new parts were balanced at the factory so it was not necessary.
Sounded suspicious to me. If nothing else, what about the weld material?

But the company had been in business for a while and did that for a living. Truck vibrated all the time.

I had some parts in a machine shop being worked on, and swung by to see if they were ready. I know the owner well, and he did all my machine work.
When I walked in, he was working on a large truck driveshaft. I had not known he did them. When he got through, he took it over to a machine and balanced it.
Had to weld a couple of washers on to get it perfect.

I went straight out and pulled my shaft off. He put it on his machine, and it took three washers, two on one end and one on the other, to get it balanced.
Naturally, he has done all my shaft work from then on.
I have since seen lots of drive shaft builders that do not bother with balancers.
 

Bent77

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Joints are slightly out of matched angle and/or tire out if balance
 

jeff in co

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Factory new, or new built? I learned about built shafts the hard way in my old Ford. I needed a new rear shaft because the splines were worn, and there was a place in town called The Drive Shaft Shop. They would cut and weld in a new spline much cheaper than factory.

I asked when I got it back if they had balanced it, and they said that the new parts were balanced at the factory so it was not necessary.
Sounded suspicious to me. If nothing else, what about the weld material?

But the company had been in business for a while and did that for a living. Truck vibrated all the time.

I had some parts in a machine shop being worked on, and swung by to see if they were ready. I know the owner well, and he did all my machine work.
When I walked in, he was working on a large truck driveshaft. I had not known he did them. When he got through, he took it over to a machine and balanced it.
Had to weld a couple of washers on to get it perfect.

I went straight out and pulled my shaft off. He put it on his machine, and it took three washers, two on one end and one on the other, to get it balanced.
Naturally, he has done all my shaft work from then on.
I have since seen lots of drive shaft builders that do not bother with balancers.

Agree. My new shaft also was out of balance. After paying for a brand new one, had to also get balanced. Frustrating to pay for balancing a brand new shaft!
 

Bent77

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Agree. My new shaft also was out of balance. After paying for a brand new one, had to also get balanced. Frustrating to pay for balancing a brand new shaft!
Spring creek 7/30?
 

Thomas Fournier

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Brand new slip yoke (spicer) brand new tube steel, brand new Spicer ends, brand new factory style 1410 spicer non-greasable u-joints. It's litterally brand new I have the old shaft in my back yard. Could this type of vibration be caused by tires? I want to say no but I just don't know. I'll call the shop to see what they think... I'll post when I find out.
 

Bent77

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Brand new slip yoke (spicer) brand new tube steel, brand new Spicer ends, brand new factory style 1410 spicer non-greasable u-joints. It's litterally brand new I have the old shaft in my back yard. Could this type of vibration be caused by tires? I want to say no but I just don't know. I'll call the shop to see what they think... I'll post when I find out.
Yeah tires can do that if they are cupped or out of balance. If the issue was not present at that speed before the driveshaft, if look there first
 

Kay86K5

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Can you upload a pic of your pinion angle on your rear axle? I'm just curious if I'm reading your OP correctly, I'm wondering if the angle is still off enough to where you should have a CV shaft instead of a normal 2 joint shaft. But we will only be able to tell that for sure with a picture. Do you have one handy to upload?
 

Bent77

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If it were mine, I'd run that pinion angle up. 4 wheel parts has pinion shims, worth a stab to see if that makes it better
 

JoshHefnerX

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Don't think it looks too far off. Is that stock height? Those angles aren't that harsh... Is there any play in the slip joint on the 241?
 

Bent77

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My driveline guy said the same thing... should I do a 3 degree?
I would chock the wheels and unbolt the shaft at the pinion. Then manipulate an angle finder (or an iphone 5 has an angle finder) and see what it looks like at 2,3, & 4°

The shims i got from them i drilled to run the spring bolt through
 
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